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  1. Deansharafi

    CTs for Reactors

    Dear all, Does anybody know if the CTs used for reactors (330KV) should have a different specification from other CTs and why? Thanks in advance
  2. Deansharafi

    Different CT Ratio for Generator Differential Protection

    It is wise to do a "Stability" test on the generator differential scheme first to establish the true nature of the problem. It can be something as simple as a reversed polarity. Be careful with CTs of different type/class, as they can always mismatch and create problems in case of a through fault.
  3. Deansharafi

    System simulation vs manual calculations

    Trying to calculate fault values on a plant you describe above will be an absolute nightmare. SKM software with 100 or 300 buses will be sufficient and is not expensive compared to the time that you must spend on hand calculations.
  4. Deansharafi

    Substation Earthing

    I confirm the above posting. For large substations the good earthing resistance value is below 0.5 ohm. I have carried out dozens of tests in transmission substations in Australia, the average value is 0.25 Ohms.
  5. Deansharafi

    Line impedance calculations

    There are formulas for calculating positive and zero sequence impedances, however if you don't know the values (positive sequence impedance is provided by the manufacturer and does not change zero sequence depends on soil quality, season etc), the best thing to do is to carry out a Line...
  6. Deansharafi

    High Voltage Lattice Tower Earthing

    Dear all, Do you know of any useful information or literature in relation to high voltage tower earthing, concept, design criteria, testing and commissioning etc. Thanks
  7. Deansharafi

    Clamp-on Ground resistance Testers

    Dear all, Anyone has any experience with clamp-on ground resistance testers? I am looking into replacing old ground resistance testers which operate on the basis of "Fall of Potential" method with clamp-on testers, which are quicker and more convenient. I appreciate if you could share your...
  8. Deansharafi

    High Voltage Substation Grounding (Earthing)

    Hello RalphChristie and others, Thanks for your responses. I am talking about 132 230 and 330KV. I have IEEE Green book and I will appreciate if you could send me the link to the ESKOM document. Merry Christmass to all.
  9. Deansharafi

    High Voltage Substation Grounding (Earthing)

    Hello alehman, I tried searching first, and I was supprised that there were nothing under "earthing" and the topics under "Grounding" was limited to one. However thanks for the advice. Do you have a link to the standard?
  10. Deansharafi

    High Voltage Substation Grounding (Earthing)

    Dear all, Do you know of any useful information or literature in relation to high voltage substation earthing, concept, design criteria, testing and commissioning etc. Thanks and merry Christmas and Happy New Year.
  11. Deansharafi

    Harmonics on HV motors

    The units are volts and amps RMS values. The measurement has been done from CTs and VTs. The fundamental voltage is 3300V and current is 100A. I don't know what sort of recorder has been used. My question is: can harmonics on current of one phase be so high without affecting harmonics on voltage...
  12. Deansharafi

    Harmonics on HV motors

    Hi all, I am investigating power recordings on a site, which does not have considerable sources of producing harmonics. However I see that there are considerable harmonics on the red phase current only which seems strange to me. There are small harmonics on voltage, which is normal and small...
  13. Deansharafi

    Harmonics on HV motors

    Hi all, I am investigating power recordings on a site, which does not have considerable sources of producing harmonics. However I see that there are considerable harmonics on the red phase current only which seems strange to me. There are small harmonics on voltage, which is normal and small...
  14. Deansharafi

    Grounded middle phase on secondary Wye CCVT

    In australia, all the middle phases are grounded and it is industry common practice, the reason being as per Discop's explanation.
  15. Deansharafi

    CT Accuracy: 5P10, 10B50 and 0.5M5

    P is designation for protection. 5P10 means that the CT will have max of 5% inaccuracy when the current of 10 times reated current of CT is experienced. M is designation for metering. 0.5M means that the CT max inaccuracy is 0.5% Never seen or heared of 10B50.
  16. Deansharafi

    Switchgear Fault Level

    Reactive, Thanks for the valuable post. Fault level is regarded the available current after normally 8 cycles. This is the value that is compared against the short circuit capacity of a switchgear. I know that the protection may break the fault current sooner than 3 seconds, however if the...
  17. Deansharafi

    Synchronous Motors

    Hi all, Do Slip ring Synchronous motors contribute to short circuit level of a power system as do induction motors? Thanks.
  18. Deansharafi

    Induction motor contribution to fault level

    Hi all, In establishing the induction motor contribution to a fault level of a system, what criteria can be considered? Are contributions of small LV (415V)motors considered significant to a fault level on an HV switchboard? These small motors normally don't have a considerable inertia and are...
  19. Deansharafi

    Zig-zag transformer winding

    ausphil, The ratings of zigzag transformers show current values such as 150A. Is this value the maximum earth fault current that is allowed to pass through transformer? What are typical Z% for this type of transformers?
  20. Deansharafi

    Switchgear Fault Level

    Hi All, How close can your fault capacity get to the fault rating of a switchboard. Let's imagin that a switchboard is rated for 30KA for 3 seconds, what fault capacity can you have on that switchboard to be safe?

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